In the assembly of snap-fit components, it is necessary to account for build variation in component location. Build variation is the stack-up of tolerances between fastener locations when two different processes are used to locate the fasteners in each component. For example, an interior door trim on an automobile may have up to ten snap-fit fasteners protruding from the back surface that are designed to have blind lead-in and assembly to ten matching holes in the sheet metal of the vehicle. Because the processes are different between the manufacturing of the door panel (often molded) and the manufacturing of the sheet metal (often punched holes) there will be variations in the locations of the holes relative to each other. To allow for assembly of the door panel to the sheet metal, the blind fasteners used between the holes of the door panel and the holes of the sheet metal are allowed to float in oversize holes on the door panel. A 1.0 to 2.0 mm float will account for build variations between the two components and has worked successfully for the installation of automobile interior door trim.
Other assemblies cannot allow float in the blind attachment arrangement due to the fit and function requirements of the components being assembled. One example of such is the attachment of vehicle tail lamps and headlamps. The components for headlamps and tail lamps require solid attachment to the sheet metal of the vehicle so that proper adjustment, positioning and aim of the lights are achieved and maintained. The use of all floating fasteners is not feasible for these types of installations. To overcome the issues surrounding build variation, tail lamps and head lamps are known to be attached at one six-way locating position (a hole) and at up to three four-way locating positions (slots). Known fasteners are configured for either holes or slots, with different fasteners used for holes (circular) and for slots (elongated). Assembly plants must maintain inventories of each, and provide each to the proper place for installation.
Another problem is encountered in some situations with known elongated fasteners secured in slots. To insert the fastener into the slot, it is necessary to properly align the fastener with the elongated slot. If the longitudinal axis of the fastener and the longitudinal axis of the slot are not aligned properly, the fastener cannot be inserted into the slot or will be inserted with great difficulty, perhaps even damaging the anchoring portion of the fastener.
Known fasteners used in holes are circular, with four anchoring legs. Circular fasteners of this type will not work well in slots. The fastener is secure only if opposed anchoring legs are transverse to the axial direction of the slot. If not, the fastener will become loose and can fall from the slot.
A preferred blind fastener can be anchored regardless of the orientation of the fastener. Blind fasteners allow for the preassembly of components and shipment of the all parts in the assembly. If a single anchoring part is used between two components, the anchoring part is assembled in one of the components, generally aligned with the anchoring location of the other components and simply pressed together. When a two-part fastener is used, one part of the fastener is located in one component and the other part of the fastener is located in the other component, with the fastener parts generally located and pressed together during final assembly. Alternatively, one component can have an assembled fastener connected to it and subsequently aligned with the other component and pushed together. Again, in any of these situations, a preferred blind fastener does not require positioning or orientation relative to the anchoring hole, but merely general alignment therewith and compression for attachment. Preferred blind fasteners can be attached from one side of the components without having to attach or modify the items from the opposite side of the components.
A preferred fastener offers rigid attachment across both holes and slots, can be provided as a part in assembly attached to one component and allows for good lead-in and assembly.